Recently, with the development of electrical and electronic devices and advanced information communication devices, the operating frequency of circuits tends to increase to a high-frequency band of several GHz, and devices tend to be multi-functional and downscaled. These devices have become seriously problematic in terms of malfunctions and signal quality degradation, which are caused by electromagnetic interference (EMI) and occurrence of noise, and human-harmful electromagnetic waves (EMWs) and the pollution of EMWs due to emission of EMWs. To solve signal quality degradation affected by secondary interference due to reflection caused by a conventional EMW shield or EMI caused by coupling between adjacent signal lines, development of a technique of absorbing EMWs using a magnetic material has become brisk.
An EMW absorbing material serves an important function to inhibit noise causing malfunctions in devices in electronic devices (e.g., circuit patterns, mounting components, cables, and the like), which have lately become more lightweight, thinner, and simpler, prevent crosstalk between circuit blocks or dielectric coupling in an adjacent substrate, and improve receiving sensitivity of an antenna, or reduce the influence of EMWs on the human body. In particular, to equally apply EMW absorbing material to electronic components used in various frequency bands, widening the frequency band of EMW absorbing is essential.
In near-field EMW absorbing technology, it is imperatively necessary to develop a chip-level ultrathin absorbing material capable of reducing not only EMI caused by multi-functional high-density mounting of components of electronic devices and single chips and an increase in frequency, but also interference between digital-analog signals, and removing EMW noise and controlling EMI to improve signal quality in a wide band of ˜GHz. Presently, in the case of the chip-level ultrathin absorbing material, there is an urgent need to take measures for EMI in a high frequency band worldwide to prevent malfunctions in electronic components and chips and signal quality degradation due to conduction noise, coupling, and electromagnetic radiation (EMR) of fine, complicated signal lines on a unit space and digital-analog interference. Furthermore, since near-field and far-field EMW absorbing technology is the kernel of advanced electromagnetic compatibility (EMC) and radio-frequency identification (RFID) and military hiding techniques, it is necessary to develop a wideband absorbing material in which new dielectric and magnetic materials are complicated.
A magnetic material having a high permeability is mainly employed to obtain a high absorbing power. However, since resonance occurs in most magnetic materials with an increase in frequency, the magnetic materials nearly lose their magnetic permeabilities in a frequency range of several GHz. Also, since a magnetic spin has directionality, fine control for absorption of EM energy is very difficult according to complicated directionality of a device or circuit. To overcome this drawback, ultrathin magnetic metal particles having a high aspect ratio are needed in terms of material shape, and techniques of orienting and dispersing metal particles in an absorbing material are also necessarily required. Meanwhile, with an increase in integration density of electronic components, effectively controlling heat generated on a chip in an EMW absorber during a process of absorbing incident EM energy and converting the EM energy into heat has become an important issue. Accordingly, it is important to design an ultrathin EMW absorbing material according to an aspect ratio of magnetic particles in a magnetic composite. In this case, the degree of technical difficulty may be regarded as very high.